Case IH F-3507-03 - ECU – Engine Control Unit (ECU) or Dosing Control Unit (DCU / DeNOx Module): Supply UB3 short circuit to battery failure

The controller is detecting voltage on the UB3 circuit (which provides power to the Coolant Control Valve and the Reverting Valve) when it should not be present. This typically means a wire is chafed and touching a 12V/24V power source, or there is an internal electrical short inside the DEF pump module or valve.

• MAGNUM AFS Connect
• Magnum AFS Connect tractors
• Steiger AFS Connect tractors
• 240 Series Axial-Flow Combines
• Puma series tractors
• Optum series tractors

1. 1

   Visually inspect the wiring harness between the ECU/DCU and the DEF Pump Module. Look specifically at the UB3 circuit wires leading to the coolant control valve and reverting valve for chafing, melting, or pinched areas that could be shorting to a battery power wire.

2. 2

   Perform a disconnect test: Disconnect the reverting valve and coolant control valve. If the active fault code changes from a 'short circuit to battery' (F-3507-03 / P20A3) to an 'open circuit' code (like P20A0 or F-3507-04), the wiring is likely fine, and the short is internal to the valve or the DEF pump module itself.

3. 3

   Check the connector pins at the DEF pump module and valves for corrosion, water ingress, or bent pins that might be bridging a power circuit to the UB3 pin.

4. 4

   With the key in the OFF position (Key 15 off), test the UB3 supply wire with a multimeter. There should be no voltage present. If voltage is present, trace the wire back to find the short.

1. 1

   Power Down

   Turn off the machine, remove the key, and disconnect the battery to prevent further electrical damage.

2. 2

   Locate Components

   Locate the DEF/AdBlue Pump Module (usually mounted near the DEF tank) and identify the Coolant Control Valve and Reverting Valve connections.

3. 3

   Repair Wiring

   If the diagnostic checks revealed a chafed wire shorting to power, cut out the damaged section, splice in a new wire, solder, and seal it with marine-grade heat shrink.

4. 4

   Replace Component

   If the short is internal (as proven by the disconnect test), replace the faulty Coolant Control Valve or the entire DEF Pump Module (the reverting valve is often integrated into the pump module).

5. 5

   Reassemble

   Reconnect all electrical connectors and reconnect the battery.

6. 6

   Clear Codes

   Use the Case IH Electronic Service Tool (EST) or the AFS Pro display diagnostic menu to clear the inactive F-3507-03 fault code.

7. 7

   System Test

   Run an SCR system prime test or dosing test via the EST to verify that the reverting valve and coolant control valve operate correctly without triggering the fault.